Personal identity instruments are widely used in society, e.g. passports, credit cards, driver's licences, building passes, etc. Such instruments are very valuable, and therefore are often illegally fabricated or stolen and altered so that they can be used fraudulently by another person. Such an instrument ideally should be useless in the hands of another person.
In order to make an instrument more difficult to counterfeit or use by another person, it bears the signature and sometimes a photograph of the owner of the instrument. A security guard, cashier, customs agent, etc. typically verifies the picture visually with the face of the user, sometimes also requests a signature for comparison with the signature on the instrument, and by that means verifies the authenticity of the instrument.
However such instruments are subject to fraud. It is possible to make a fake instrument from a stolen document or card containing a different photograph, matching the fraudulent holder.
U.S. Pat. No. 5,027,113 describes a process and apparatus for making a personal identification instrument which is subject to machine verification. An instrument according to that patent is first made carrying e.g. indicia and/or a photograph, and deviations from a standard of the outlines of at least some of the indicia (on a magnified scale) are stored in a memory. When an instrument is presented, a machine reads the exact outline of corresponding indicia. Since paper fibers, ink bleeds, etc. result in a different outline than the original, the machine comparing the deviation data with the originally stored outline deviation data can result in the declaration of a fraudulent instrument.
Similarly, for verification of a photograph, the entire photograph is read by a camera. The variation of the distribution of grey levels in the image scanned by the camera, as compared with stored data describing the variation of the distribution of grey levels, stored from the original authentic photograph, can result in detection of a fraudulent instrument.
Unfortunately the system described in the patent requires storage of a large amount of data for each instrument, which becomes very large when photograph data are stored. In addition, each verification station requires access to the stored data. While the data can be stored in a centralized data bank, verification requires the transfer of very large amounts of data along transmission lines from the central data bank to the verification stations. Where there is a continuous flow of persons to be authenticated, for example where many millions of passport-holding persons are subject to verification at any of hundreds of border points spanning very long borders (e.g. the border between the United States and Canada, the border between the United States and Mexico) the cost of using such a system becomes prohibitive.